Molding compositions comprising acetal polymers have been in commercial use for many years. They have application in a wide variety of end uses e.g., automobile applications such as bumper extensions and instrument panels, plumbing supplies such as valves, shower assemblies, flush tank components, faucets and pipe fittings, tool components such as screw driver adaptors, and household and personal products, such as quick boiling electric water kettles, clothes hangers and combs.
Acetal polymers have a highly favorable spectrum of physical properties which are responsible for their wide commercial acceptance. However for certain molding applications, e.g., exterior automobile body parts, molding compositions that impart higher than usual impact strength to articles molded from them are highly desirable.
Application Ser. No. 625,954, filed June 29, 1984, by Drzal et al. and now abandoned, the entire disclosure of which is incorporated by reference, discloses molding compositions having improved impact strength comprising a blend of an acetal polymer with any of certain elastomeric polyurethanes. In particular, the application discloses compositions having improved impact strength at low temperatures, i.e., as low as -20.degree. F. or lower.
U.S. Pat. No. 4,096,202, of Farnham et al., the entire disclosure of which is incorporated by reference, discloses the enhancement of the impact strength of poly(alkylene terephthalates) by blending with a multiphase composite interpolymer.
U.S. Pat. No. 4,179,479 of Carter, the entire disclosure of which is incorporated by reference, discloses polymer blends of 40 to 99% of a thermoplastic polyurethane, 1 to 60% of a thermoplastic polymer which can be a polyoxymethylene, and 0.5 to 10% of an acrylic polymer as a processing aid. The blend is stated to provide a more homogeneous melt and enhanced hot metal release and lubricity.
Although the described polymeric additives for the improvement of the impact strength of acetal polymers are generally beneficial, any means for obtaining an even greater enhancement of impact strength than can be obtained by the conventional use of the additives would be highly desirable. This applies particularly to any improvement in impact strength which can be obtained without increasing the total amount of additive blended with the acetal polymer.